Decontaminating products from pyrolysis of chcif2



' Patented June 26, 1951 DECONTAMINATING PRODUCTS FROM PYROLYSIS 0FCHClF-z William S. Murray, Wilmington, Del., assignor to E. I. du Pontde Nemours & Company, Wilming'ton, Dcl., a corporation of Delaware NoDrawing. Application April 21, 1948, Serial No. 22,491

Claims.

This invention relates to decontaminating products obtained in thepyrolysis of CHClFa and particularly to rendering innocuous the toxicimpurities present in the higher boiling products obtained in thepyrolysis of CHClFz.

Downing et al., in Patent 2,384,821 granted on September 18, 1945, andPark et al., in an article Synthesis of Tetrafluorcethylene, ap-

pearing on pages 354 to 358, inclusive, of In-' dustrial and EngineeringChemistry, vol. 39, No. 3, for March, 1947, disclose the pyrolysis ofCHCIF'z at temperatures of from about 600 C. to about 1000 C. to produceC2F4 (tetrafluoroethylene) and higher boiling fluorinated productscommonly referred to as high boilers. Upon removal of acids, the C2F4and unreacted CHC1F2 from the pyrolysis mass, the high boilers" areobtained as a residue, amounting to about 20 pounds to about 35 poundsfor every 100 pounds of 02F; produced, which boils above .4.0 0.,generally in the range of from about 30 C. to about 200 C. Such residueis a mixture of highly fluorinated straight-chain and cyclic aliphaticcompounds, the boiling points of the individual members thereof varyingfrom about 30 C. to about 228 C. Over 97% of such high boiler residue ismade up of such stable and non-toxic compounds as CHF2--CC1F2, cyclicClFa and compounds of the series represented by the formula H(CF2)1.C1wherein it varies from 3 to 14. Such residue, or mixture of higherboiling compounds, and the various fractions and components thereof willbe hereinafter referred to, for convenience, as high boilers.

The high boiler residue or mixture is contaminated with from about 2% toabout 3% of.

highly toxic compounds which are characterized by a pungent odor. Thesetoxic compounds have not been positively identified and their chemicalconstitutions and structures have not been exactly determined. 'Theyaredefinitely known to be highly fluorinated organic compounds, at leastsome of which contain chlorine. They appear to contain a cyclicstructure. The boiling points and tentatively assigned formulae of someof such toxic compounds are disclosed in the article by Park et al.hereinbefore referred to, and particularly in Table II' on page 358.

These toxic compounds render the vapors of the high boilers containingthem so toxic on inhalation as to make extremely hazardous the handlingof the material for any further desired processing or their disposal aswaste materials. This is demonstrated by the fact that test rats, whenexposed to air containing about 3% by volume of the contaminated highboilers for 15 minutes, died within an hour from severe.

hemorrhagic pulmonary edema. Such toxic compounds cannot be separatedfrom the high boilers by fractional distillation, apparently becausethey form azeotropes with constituents of the high boilers, and appearin substantially. all fractions of the high boiler mixture obtained byfractional distillation.

It is an object of the present invention to provide an economical,efiicient, commercially practicable method for rendering the toxiccompounds in the high boilers innocuous. other object is to provide amethod of rendering the toxic compounds innocuous and removing them fromthe high boilers. Further objects are to advance the art. Still otherobjects will appear hereinafter. I

The above and other objects may be accomplished in accordance with myinvention which comprises mixing at least 3% by weight of anhydrousammonia with the pyrolysis products which boil in the range of fromabout -3D C. to about 228 0., obtained in the pyrolysis CHC1F2 attemperatures of from about 600 C. to about 1000 C., and which containtoxic impurities, in the liquid phase at temperaturesof from about C. toabout 50 C., and maintaining the ammonia in admixture with the liquidpyrolysis products under such conditions until reaction of the ammoniawith the toxic impurities is substantially complete. I have found thatanhydrous ammonia reacts spontaneously and with the evolution ofconsiderable heat with the impurities in the high boilers attemperatures as low as 75 C. to form innocuous brown compounds which aresolid at ordinary temperatures and insoluble in the high boilers and inwater, but which are fairly soluble in methanol. If it is desired torecover constituents of the high boilers, the ammonia reaction productsmay beseparated therefrom by filtration, fractional distillation,extraction with solvents or the like. If the "constituents of the highboilers are not to be recovered but are to be disposed of as waste, thenthe decontaminated material may be safely discarded as such. However, insuch latter case, it will generally be preferred to mix thedecontaminated material with methanol or other solvent for the ammoniareaction products or to carry out the decontamination in the presence ofsuch solvent so as to facilitate the discharge of the decontaminatedmaterial from the reaction vessel and its subsequent disposal.

The high boilers, which are to be treated in accordance with myinvention, may be the residue obtained after removal of the acidic con-An- I assess-4 stituents, the tetrafluoroethylene and any unreactedCHClFa. Alternatively, such residue may be subjected to one or morefractional distillations and then the treatment applied to each fractionwhich contains the toxic compounds.

At least about 3% by wei ht of anhydrous ammonia, based on the highboilers" treated, is required for reaction with the toxic compounds.

Preferably, an excess of ammonia, from about 5% to about by weight, isemployed. Much larger excesses of ammonia can be used, if desired, butsuch larger excesses have the disadvantage of requiring larger equipmentand the recovery of such larger amounts of ammonia. The liquid highboilers may be added to the liquid ammonia or the ammonia may be addedto the high boilers.

The process has been carried out successfully at -75 C. and at 50 C.Preferably, it will be carried out at temperatures of from about C. toabout 50 C. While reaction may be carried out at temperaturessubstantially above 50 C., such higher temperatures will be generallyundesirable because of the high pressures that would be required tomaintain the reaction in the liquid phase and to maintain the ammonia ineffective contact with the "high boilers. Ammonia is somewhat soluble inthe high boilers. Since the reaction takes place spontaneously uponmixing the liquids, pressure is without influence on the reaction andhence only such pressures as will maintain the reactants in contact inthe liquid phase will be required. The reaction takes place in theliquid phase only. All efforts to decontaminate the high boilers in thevapor phase, even at temperatures as high as 500 0., were unsuccessful.-

Usually, where constituents of the high boilers are to be recovered, itwill be preferred to employ substantially pure anhydrous ammonia.However, even where constituents of the high boilers are to berecovered, it will some times be found desirable to carry out thereaction in the presence of methanol or other, solvent for the ammoniaand the reaction products. This serves to lower the ammonia pressure andto facilitate discharge of the decontaminated material from the reactionvessel and transportation to other apparatus for further processing. Inorder to effect reasonable solution of the reaction products, from about3 to 6 gallons of methanol per 100 pounds of the high boilers (fromabout 19% to about 40% by weight) should be used. Larger amounts ofmethanol may be used, if desired. Aqueous solutions, includingconcentrated ammoniumhydroxide, are ineffective and hence the presenceof any substantial amount of water must be avoided.

In order to more clearly illustrate my invention and preferred modes ofcarrying the same into effect, the following examples are given:

Example 1 a To 360 g. of high boiler residue in a 600 cc. steel cylinderwas added 16 g. of anhydrous ammonia (4.25% by weight). After standingfor 28 hours, a liquid phase sample was scrubbed by passing the vaporthrough water, dried with 09504 and tested on rats. After an 8 minuteexposure period, the rats were killed and examined; their lungs showedslight congestion but no gross edema. A similar sample, taken afterstanding 28 days, produced only a slight discoloration and congestionwhen similarly tested. Another sample, treated with 3.1% by weight ofammonia for 50 hours, produced no gross pathol- 4 ogy. A sample of theuntreated high boilers, scrubbed, dried and tested in the same manner asthe ammonia treated ones, produced marked edema, areas of hemorrhage andgeneral congestion. In all these tests, the air contained about 5% byvolume of high boiler" vapor.

Example 2 To an evacuated 5 gallon steel autoclave equipped with brinecooling, plow type a tation, and the usual vapor and standpipeconnections, etc., was added one gallon of methanol and 2 pounds ofanhydrous ammonia. The pressure in the autoclave, at a liquidtemperature of 4 0., was 8 p. s. i. a. A total of 24 pounds of toxichigh boiler residue was then added at an average rate of 1 pound perminute. Within a half hour after the addition had been completed, thedecontaminated liquid was sampled, scrubbed by passing the vapor throughwater, dilute sulfuric acid, and water again (to remove methanol andexcess ammonia), dried with 02504 and later tested for toxicity. As aresult of this ammonia treatment, the test rats, instead of sufferingfrom severe pulmonary 'hemorrhagic edema. were found to be, for allpractical purposes, perfectly normal after a 6 minute exposure to aircontaining 4% by volume of the decontaminated material.

It will be understood that the preceding examples are given forillustrative purposes solely and that my invention is not to be limitedto the specific embodiments disclosed therein. Within the scope of thisdisclosure, as heretofore given, it will be evident that the proportionsof reactants and solvent, the temperatures, pressures, order of steps,apparatus and the like may be varied as desired. Also, any desiredfraction may be separated from the "high boiler residue and treated inaccordance with the principles of my invention.

Since the most characteristic pr perty of highly fluorinated aliphaticcompounds is their unusualstability and inertness to chemical reaction,it was wholly surprising to find that the toxic impurities in the highboilers" would react with ammonia and, particularly, so remarkablyspontaneously. It was also quite surprising to find that the reactionwould take place only in my invention provides a commerciallypracticable and economical process for decontaminating the highboilers."

I claim:

1. The process for decontaminating the pyrolysis products which boil inthe range of from about 30 C. to about 228 0., obtained in the pyrolysisof CHCIF: at temperatures of from about 600 C. to about 1000 C., andwhich contain highly fluorinated organic toxic impurities,

which process comprises'mixing the pyrolysisproducts in the liquid phaseat temperatures of from about --'75 C. to about 50 C. with at least 3%by weight of anhydrous ammonia, and maintaining the ammonia in admixturewith the liquid pyrolysis products under such conditions until reactionof the ammonia with the toxic impurities is substantially complete.

2. The process for decontaminating the pyrolysis products which boil inthe range of from about -30 C. to about 228 C., obtained in thepyrolysis of CHClFz at temperatures of from about 600 C. to about 1000C., and which contain highly fiuorinated organic toxic impurities, whichprocess comprises mixing the pyrolysis products in the liquid phase attemperatures of from about -'75 C. to about 50 C. with from 3% to about10% by weight of anhydrous ammonia, andmaintaining the ammonia inadmixture with the liquid pyrolysis products under such conditions untilreaction of the ammonia with the toxic impurities issubstantiallycomplete.

3. The process for decontaminating the pyrolysis products which boil inthe range of from about 30 C. to about 228 C., obtained in the pyrolysisof CHClFz at temperatures of from about 600 C. to about 1000 C., andwhich contain highly fluorinated organic toxic impurities. which processcomprises mixing the pyrolysis products in the liquid phase attemperatures of from about 75 C. to about 50" C. with from about toabout by weight of anhydrous ammonia, and maintaining the ammonia inadmixture with the liquid pyrolysis products under such conditions untilreaction of the ammonia with the toxic impurities is substantiallycomplete.

4. The process for decontaminating the pyrolysis products which boil inthe range from about 30 C. to about 228 C., obtained in the pyrolysis ofCHClF2 at temperatures of from about 600 C. to about 1000 C., and whichcontain highly fiuorinated organic toxic impurities, which processcomprises mixing the pyrolysis products in the liquid phase attemperatures of from about C. to about 50 C. with at least 3% by weightof anhydrous ammonia, and maintaining the ammonia in admixture with theliquid pyrolysis products under such conditions until reaction of theammonia with the toxic impurities is substantially complete.

5. The process for decontaminating the PV- rolysis products which boilin the range of from about 30 C. to about 228 C., obtained in thepyrolysis of CHClFz at temperatures of from about 600 C. to about 1000C., and which contain highly fiuorinated organic toxic impurities,

which process comprises mixing the pyrolysis products in the liquidphase at temperatures of from about -20 C. to about 50 C. with from 3%to about 10% by weight of anhydrous ammonia, and maintaining the ammoniain ad-- mixture with the liquid pyrolysis products under such conditionsuntil reaction of the ammonia with the toxic impurities is substantiallycomplete.

6. The process for decontaminating the pyrolysis products which boil inthe range of from about 30 C. to about 228 C., obtained in the pyrolysisof CHClFz at temperatures of from about 600 C. to about 1000 C., andwhich contain highly fluorinated organic toxic impurities, which processcomprises mixing the pyrolysis products in the liquid phase attemperatures of from about -20 C. to about 50 C. with from about 5% toabout 10% by weight of anhydrous ammonia, and maintaining the ammonia inadmixture with the liquid pyrolysis products under such conditions untilreaction of the ammonia with the toxic impurities is substantiallycomplete.

7. The process for decontaminating the pyrolysis products which boil inthe range of from about -30" C. to about 228 C., obtained in thepyrolysis of CHClFz at temperatures of from about 600 C. to about 1000C., and which contain highly fiuorinated organic toxic impurities, whichprocess comprises mixing the pyrolysis products in the liquid phase attemperatures of from about 75" C. to about 50 C. with at least 3% byweight of substantially pure anhydrous ammonia, and maintaining theammonia in admixture with the liquid pyrolysis products under suchconditions until reaction of the ammonia with the toxic impurities issubstantially complete.

8. The process for decontaminating the pyrolysis products which boil inthe rangeof from about -30 C. to about 223 C., obtained in the pyrolysis'of CHClF2 at temperatures of from about 600 C. to about 1000 C., andwhich contain highly fiuorinated organic toxic impurities, which processcomprises mixing the pyrolysis products in the liquid phase attemperatures of from about 20" C. to about 50 C. with from about 5% toabout 10% by weight of substantially pure anhydrous ammonia, andmaintaining the ammonia in admixture with the liquid pyrolysis productsunder such conditions until reaction of the ammonia with the toxicimpurities is substantially complete.

9. The process for decontaminating the pyrolysis products which boil inthe range of from about 30 C. to about 228 C., obtained in the pyrolysisof CHClFz at temperatures 'of from about 600 C. to about 1000 C., andwhich contain highly fluorinated organic toxic impurities,

'which process comprises mixing the pyrolysis products in the liquidphase at temperatures of from about -75 C. to about 50 C. with at least3% by weight of anhydrous ammonia dissolved in from about 19% to about40% by weight of methanol based on the pyrolysis products, andmaintaining the ammonia in admixture with the liquid pyrolysis productsunder such conditions until reaction of the ammonia with the toxicimpurities is substantially complete.

10. The process for decontaminating the pyrolysis products which boil inthe range of from about 30 C. to about 228 C., obtained in the pyrolysisof CHClF2 at temperatures of from about 600 C. to about 1000 C., andwhich contain highly fiuorinated organic toxic impurities, which processcomprises mixing the pyrolysis products in the liquid phase attemperatures of from about 20 C. to about 50 C. with from about 5% toabout 10% by weight of anhydrous ammonia dissolved in from about 19% toabout 40% by weight of methanol based. on the payrolysis products, andmaintaining the ammonia in admixture with the liquid pyrolysis productsunder such conditions until reaction of the ammonia with the toxicimpurities is substantially complete.

WILLIAM S. MURRAY.

Name Date Downing et al. Sept. 18, 1945 Number

1. THE PROCESS FOR DECONTAMINATING THE PYROLYSIS PRODUCTS WHICH BOIL INTHE RANGE OF FROM ABOUT -30* C. TO ABOUT 228* C., OBTAINED IN THEPYROLYSIS OF CHCIF2 AT TEMPERATURES OF FROM ABOUT 600* C. TO ABOUT 1000*C., AND WHICH CONTAIN HIGHLY FLUORINATED ORGANIC TOXIC IMPURITIES, WHICHPROCESS COMPRISES MIXING THE PYROLYSIS PRODUCTS IN THE LIQUID PHASE ATTEMPERATURES OF FROM ABOUT -75* C. TO ABOUT 50* C. WITH AT LEAST 3% BYWEIGHT OF ANHYDROUS AMMONIA, AND MAINTAINING THE AMMONIA IN ADMIXTUREWITH THE LIQUID PYROLYSIS PRODUCTS UNDER SUCH CONDITIONS UNTIL REACTIONOF THE AMMONIA WITH THE TOXIC IMPURITIES IS SUBSTANTIALLY COMPLETE.